Method and apparatus for minimizing sound



Feb. 14, 1933. P. E. GOOD 1,897,649

METHOD ,AND APPARATUS FOR MINIMIZING SOUND Filed Dec. 21, 1929 2Sheets-Sheet 1 2 0 gljjTOR Patented Feb. 14, 1933 UNITED STATES PAUL EaGOOD, OF RIVERTON, NEW JERSEY, ASSIGNOR T0 ELLIOTT COMPANY, OE

PATENT OFFICE JEANNETTE, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIAMETHOD AND APPARATUS FOR MINIMIZING SOUND Application filed December 27,1929. Serial No. 416,866.

The present invention relates broadly to the art of air handling inconnection with blowers, compressors and the like, and more particularlyto an improved method and apparatus for mufiling or dampening soundwaves set up in the air stream by such air handling mechanisms. Forpurposes of a clear understanding of the invention it will be describedin connection with a blower, although it will be understood that theutility of the invention is not limited with respect to the particularconstruction or type of apparatus with which it is utilized.

Air entering a blower inlet, regardless of the care which is taken inthe design of the blower itself, necessarily encounters some shock uponentering a rapidly rotating impeller. It is impossible by any means ofdesign now known to completely avoid this shock and particularly withvariable loads. It is likewise diflicult, if not impossible, to designan apparatus which will carry even a fixed load without producing somenoise.

The impact and the shock of the air produced by the rotating impellersets up eddies and, in addition thereto, also produces noise;

which is itself one form of wave vibration. The noises so produced maybe of various itches and are exceedingly objectionable. nasmuch as thevelocity of the air entering the blower impeller is below the acousticvelocity, the noise is transmitted backwardly through the air stream.

The present invention, therefore, has for one of its objects theprovision of an improved construction such that the backward travel ofsuch sound waves is interfered with or prevented to such an extent thatobjectionable noise is eliminated.

In the accompanying drawings I have shown for purposes of illustrationonly, a preferred embodiment of the present invention.

In the drawings, Figure 1 is a front elevational view of one form ofmufiiing unit constructed in accordance with the present invention,

Figure 2 is a detail top plan view, on an en-' larged scale, of aFigure3 is a diagrammatic view, partly in sepition, illustrating onetype of blower inta e, 1

Figure 4 is a partial sectional view through a plurality of units inoperative position within an intake as illustrated in Figure 3,

Figure 5 is a diagrammatic side eleva tional View of one form ofapparatus for producing mufliing strips of the character illustrated inFigure 2, and

Figure 6 is a top'plan view of the construction illustrated in Figure 5.

Since sound is definitely known to be a wave phenomenon, baffling isrecognized in the art as one means of producing silencing. The presentinvention utilizes bafiiing for the entering air such that the directionof the wave motion may be interfered with and the sound energydissipated. High pitched noises, which are produced by extremely shortsound waves, are the most objectionable to the ear, the most irritatingto the nerves and the most penetrating The present invention providesmeans for effectively eliminating sounds of this character.

v In carrying out the present invention, I preferably proceed in themanner illustrated diagrammatically in Figures 5 and 6. In accordancewith this disclosure, I take a strip S of relatively soft steel orsimilar material and pass it between corrugating rollers 2 and 3 havingteeth 4 extending at an angle of approximately 45 to the axis ofrotation and'of such construction as to provide a sufficient spacetherebetween for the reception of the material. It will be apparent thatafter the strip has passed between the corrugating rolls it assumes acontour such as illustrated in Figures 1 and 2.

The length of the strip may initially be chosen with respect to the sizeof the unit which it is desired to produce. The necessary amount ofcorrugating material having been formed, it is matched with a spacingstrip 5 having a width substantially equal to the width of thecorrugated strip, but being substantially flat in cross section. Thespacing strip 5 and the corrugated strip are then wound, in any desiredmanner, into the form of a unit substantially as illustrated in .twounits U and Figure 1, havin an outside diameter correlated to the insi ediameter of the air intake 6 in which it is to be ositioned. After theunits have been forme they may be held in assembled relationship in anydesired manner. The desired number of units having been constructed inthe general manner referred to, they may be inserted in the intake ofthe blower or other device in the general manner illustrated in Figure3. From this figure it will be apparent that adjacent units are reversedone with respect to the other so that the air entering the intake issubjected to re eated changes in direction each equal to su stantially90, the actual air flow at any instant being at an angle ofapproximately 45 to the axis of the intake or to the axis of the unitsas a whole. I

This conditionis illustrated in detail in Figure 4; in which the arrowsA represent the direction of flow of a given portion of the air. In thisfigure there are illustrated the axes of the units being illustrated bythe line ab. During travel of the air through jzhe unit U, it flows atan angle of to this axis. At the junction point between the two units itis deflected by an amount equal to twice the angle of obliquity of theindividual corrugat ons, and j thereby caused to travel through the unitU in a direction substantially normal to its direction of travel throughthe unit U.

Durin the time that the air is being trans- -,mitted t rough thesilencer in the general manner illustrated in Figure 4, sound is .beingtransmitted through the same path but in the opposite direction.

In the transmission of sound in an air =columnthere; are three phenomenawhich must be considered. The first of these is reflection, the secondrefraction, and the third diffraction, The present silencer isconstructed with respect to each of these phenomena.

Considering first the phenomenon of re flection as ap licable to soundwaves, it is well known t at waves are reflected backward from a surfaceagainst which they impinge by reason of the elastic nature of the air.The reflection is such that its angle is always exactly equal to theangle of incidence. With this general statement,it may be assumed thatsound waves are travelling backwardly in' the eneral direction indicatedby the arrows in Figure 4. It will be apparent that this direction is atexactly 90 to the up stream side of the corrugations 4'. This beingtrue, the sound is reflected.

backwardly into the air column exactly in the direction from which itarrived. This I tendency of the silencer toreflect the sound backwardlyin exactly the same path as that from which it has come constitutes oneof the features of the present invention.

Considering the question of refraction, it

is well known that when sound is travelling 1n a medium such as air, andthe air undergoesa change of velocity, there is a change 1n direction.When the air stream turns at the junction between the units U and U, theinertia of the air tends to eflect a compression, and sound, by theprocess of refraction, is transmitted around the corner.v In thistransmission around the corner, however, the

a repetition of the previous conditions but.-

in the opposite direction. In other words, the process of refractioncontinuously a ds the sound waves to turn the corners provided, but inbeing refracted around such co'rners, refraction takes place to agreater degree than if there' was no chan e of density in the air streamdue to centrifugal force.

As a consequence, the construction illustrate ed from the standpoint ofrefraction complicates the passage of sound waves so that they have noopportunity to be transmitted backwardly through any air column efl'ect.The result of the construction, therefore, is such as to produce evengreater complications in the refraction path. 7

Coming now to the question of diflraction, while it is true that themajor portion of the solmdwave travel is in a straight line, there is acontinuous transmission of energy to a which must be taken into accountif silence is to be considered. It is also more decidedly a significantfactor with high pitched notes than with notes of low pitch. Byproviding a curved and involved path of the character herein referredto, diffraction is made much more difiicult.

Units of the. character herein described can be readily andinexpensively made in any desired sizes and shapes such that they may bequickly assembled in the desired relationshlp to function .as asilencing medium. When so assembled they producea multiple reflection ofsound backward in the direction of propagation in a sinuous path offlow. The number of units may be varied- 1&5

rule, however, it will, be found that the higher the pitch of the notesbeing dealt with, the greater the number of units required.

I have herein considered the henomena of reflection, refraction and diraction of sound. The present structure, however, lends itself admirablyto the utilization of materials such that sound may be minimized byabsorption. If it is desired to make use of this phenomenon, the stripmaterial S, utilized for the formation of the corrugations, may be ofpapier mach or of metal with a suitable absorbing coating appliedthereto. This coating could obviously be of a rough material applied inseml-liquid form, or it could be in the nature of a woven fabriccompletely covering the same. In any event, the construction would besuch that the material itself'constituting the main portion of each ofthe units would ossess absorbing characteristics. In suc case it wouldalso be desirable to construct the spacthe opening in the adjacentelement.

ers 5 of similar material so as to gain all the advantage possible fromabsorption.

In Figure 1, one of the units is illustrated as having bracing means 7extending in a generally radial direction. Such spacing means are notillustrated in Figure 4. It is apparent, however, that where they areprovided they will tend to provide a slight space between adjacent unitswhich might in some cases bedesirable. It is obvious thatthe-corrugations would not necessarily register as accurately asillustrated in Figures 3 and 4 and that in many cases at least the edgeof one corrguated strip would lie directly ova; slight space between theunits such as would be afforded by the reinforcing means 7 would provideagainst restriction in the airflow at points where the-air is deflectedthrough substantia-lly 90. Where the units are constructed with respectto absorption properties, the rods 7 would be of similar construction.This could be accomplished by utilizing ordinar electrical wire, forexample, having a fa ric or rubber coating thereon.

The center plug 8 illustrated in Figure 1 is desirable for two reasons.In the first place, it prevents the formation of a continuously opencore through which sound waves could directly travel, and it provides acenter on which the corrugated material may be conveniently wound. Incase of a structure designed with respect to absorption properties,

V this plug would naturally be so selected as to likewise possess thedesired degree of absorption.

Also, where the phenomenon of absorption is depended upon for themaximum benefits, the intake 6 may be of special construction such asobtained by a proper choice of material for the intake itself or by thea plication of a suitable coating or lining 9 thereto.

While I have herein illustrated and described a preferred embodiment ofthe present invention, it will be understood that changes in theconstruction, arrangement and contour of the individual parts and unitsmay be made therein without departing either from the spirit of thepresent invention or the scope of my broader claims.

I claim:

1. In the method of preventing noise transmission, the steps comprisingdividing an air flow into a series of separate air streams radially andcircumferentially spaced, and subjecting the entire body of said airstreams to repeated and successive changes in direction eachsubstantially equal to 90.

2. In the method of preventing noise transmission, the steps comprisingproducing an air flow in a generally axial direction, dividing the flowinto a series of individual streams each progressing in an axialdirection, and deflecting the entire flow of the individual streams atfrequent and successive intervals by such an amount that the actualdirection of travel at any time after initial deflection is atsubstantially 45 to said axial direction.

3. Silencing means for sound Waves, comprising a unit including acorrugated striplike body having corrugations extending at an angle ofsubstantially 45 to its side edges.

4. Silencing means for sound waves, comprising a unit includingsuperimposed layers of strip having corrugations extendin at an angle ofsubstantially 45 to the side e ges of said strip, and a spacing stripintermediate successive layers.

5. As an article of manufacture, a sound silencing unit comprisingsuperimposed layers of strip material having corrugations formedtherein, each extending at substantially 45 to the side edges, andsubstantially smooth sided spacing strips intermediate the successivelayers.

6. Silencing means, comprising a series of axially arranged, individualand readily separable units each including corrugated members havingside edges and havin corrugations extending at an angle of su stantially45 to both of the side edgesof the members with the successive unitsreversed side for side to dispose the corrugations in successive unitsin opposite directions.

7 As an article of manufacture, a sound silencing unit, comprisingsuperimposed spirallywound layers ofistrip material having soundabsorption characteristics, the superimposed layers extending incompletely overlapping relationship with the plane of the edges ofsuccessive convolutions of each layer normal to the general direction offluid flow through the unit.

8. As an article of manufacture, a sound silencing unit comprisingcompletely superimposed co-extensive layers of strip material havingsound absorption characteristics,

said material having a series of corrugations formed therein with eachcorrugation extending generally transversely of the strip material.

9. As an article of manufacture, a sound silencing unit, comprisingsuperimposed layers of strip material having sound absorptioncharacteristics, said material having' a series of corrugations formedtherein, with each corrugation extending at an angle of substantially 45to each of the side edges of the strip material.

10. Silencing means, comprisinga series of identical units each unitcomprising a plurality of superimposed layers of strip material havingabsorption characteristics, said units being axially alined withalternate units reversed side for side, said units being constructed toprovide a tortuous fiow path therethrough with the plane of the edges ofall ofthe units substantially normal to the general direction of fluidflow through the silencing means.

25 11. Silencing means, comprising a series of similar units eachincluding superimposed layers of strip material having aborptioncharacteristics, said units being constructed to each provide a seriesof separate tortuous so flow paths therethrough in each of the layers,the flow path in each of the units extending at an angle ofsubstantially 90 to the flow path of adjacent units.

12. Silencing means for sound waves, comprising a substantiallycylindrical unit including alternate layers of corru ated strip- 7 likematerial and substantiallymaterial, the corrugations in said strip-likematerial extending at an angle of substantially 45 to the opposite sidesof the striplike material.

13. Silencing means for sound waves, comprising asubstantially-cylindrical unit ineluding a solid core having spirallywound therearound' in alternate layers a spacing strip of substantiallyflat material, and a corrugated strip, with the corrugations in saidlast mentioned strip extending at an angle of approximately 45 .to itsedge portions.

so In testimony whereof I have hereunto set I my hand. v PAUL E. GOOD. I

at spacing: I

